1 p 

 p + -~-pU = constant 



dx 



» u dF = 



[7] 



A negative pressure gradient is favorable and a positive pressure gradient 

 adverse for preventing separation of flow. 



Within the boundary layer the velocity u is zero at the surface, 

 since no slippage occurs, and increases to U at the outer edge of the boundary 

 layer. This variation of u with y, or the velocity profile, is very important 

 in the study of boundary layers. In the case of turbulent boundary layers, 

 the following power law variation gives an excellent approximation for most 

 flow conditions, and a rough approximation for strong adverse pressure 

 gradients. 



u " \ti 



where the value of the exponent n depends on the previous development of flow 

 in the boundary layer. 



Potentiol Flow 



%• 7^^ ' 



*, d* > Adverse Pressure Grodient 



'^ 



■°* 



Figure 2 - Typical Boundary Layer Around a Body of Revolution 



